Applicant claims priority under 35 U.S.C. xc2xa7119 of Austrian Application No. A 1311/99 filed Jul. 29, 1999. Applicant also claims priority under 35 U.S.C. xc2xa7365 of PCT/AT00/00199 filed Jul. 18, 2000. The international application under PCT article 21(2) was not published in English.
1. Field of the Invention
The present invention relates to a process for powder metallurgic manufacture of a coupling body having a crown of coupling teeth, whose flanks coming out from wedge-shaped end faces are in relief, such that a formed body with coupling teeth, which have wedge-shaped end faces, but axis-parallel flanks, is pressed out of a sintering powder and is sintered to a molded blank, whose coupling teeth, for forming the flank reliefs are subjected to axial compression-molding between two form tools on the one hand for the wedge-shaped end faces and on the other hand for the flank reliefs.
2. Description of the Prior Art
Coupling bodies for vehicle gearboxes have a crown of coupling teeth which cooperate with the claws of a clutch collar. For this purpose on the side facing the clutch collar the coupling teeth form roof-like, wedge-shaped end faces, which facilitate engagement of the claws of the clutch collar in the tooth crown of the coupling body. The engaged position is ensured by a flank relief of the coupling teeth. To avoid the wedge-shaped end faces and the flank reliefs having to be machined down, it has already been proposed (DE 38 39 800 A1) to manufacture these coupling bodies by powder metallurgy, such that a sintering powder is used to press out a formed body with coupling teeth which have wedge-shaped end faces, but axis-parallel flanks. Following a sintering procedure the molded body is calibrated between two form tools, and with simultaneous formation of the flank reliefs of the coupling teeth. For this purpose, the molded blank is laid in the form tool forming a bottom ram for the wedge-shaped end faces, before the top ram, which exhibits the negative form required for the flank reliefs, is pressed against the bottom ram, such that the flanks of the coupling teeth are in relief by corresponding compression molding. The drawback to this known process however is that the joint face between the form tools causes the danger of a burr-like projection in the transition region between the wedge-shaped end faces and the flank reliefs, so that these coupling bodies must be subjected to subsequent processing to be able to ensure coupling teeth without burr.
The object of the invention therefore is a process for powder metallurgic manufacture of a coupling body with a crown of coupling teeth of the type described at the outset, such that with compression molding the sintered molded blanks for forming the flank reliefs the mechanical molding procedure can be terminated, such that subsequent processing on the form is not required.
The invention solves this task by the fact that with compression molding of the flank reliefs in the transition region between the flanks and the wedge-shaped end faces a flank-side interlocking shoulder with a rounded transition to the wedge-shaped end faces and lying in the molding surface of the form tools is impressed in the flanks of the coupling teeth.
Because a flank-side interlocking shoulder is impressed, no burred heaping up of material hampering the engaging movement of the claws of the clutch collar can occur in the transition region from the wedge-shaped end faces to the flanks, particularly since compression molding provides a rounded transition of the shoulder lying in the molding surface of the form tools to the next wedge-shaped end face, so that a constant transition, advantageous for the switching procedure from the wedge-shaped end faces to the shoulder regions can be ensured. It is essential that the material is prevented from heaping up in this region by impressing the interlocking shoulders, such that the elastic behavior of the material can not be considered, particularly since the interlocking shoulders themselves no longer have any influence on the engagement movement of the claws of the clutch collar in the crown of the coupling teeth.
Since the flank-side impressed shoulders are supposed to avoid material heaping up and protruding into the path of the claws of the clutch collar, the penetration depth of the tool forming the shoulders can be comparatively slight. However, there needs to be an adequate heel there to also ensure the desired effect under series manufacturing conditions. For this reason it is recommended to impress the shoulders in the transition region between the flanks and the wedge-shaped end faces of the coupling teeth with a minimum height of 0.01 mm, in such a way that sich an advantageous region of up to 0.1 mm results for the shoulder height measurable on the form tools.